The present application relates to a transmitting and receiving system, a transmitting apparatus, a transmitting method, a receiving apparatus, a receiving method, and a program. More specifically, the application relates to a transmitting and receiving system, a transmitting apparatus, a transmitting method, a receiving apparatus, a receiving method, and a program capable of fast resuming data transmission quality during recovery from a degraded state to a normal state based on a transmission control state before the degradation in consideration for radio variations and radio link control.
In due course of progress in the recent home networking and increasing need for radio communications (e.g., cellular network, radio LAN (Local Area Network), and UWB (Ultra Wide Band)), there is expected an increasing demand for streaming reproduction of high-quality audiovisual data via radio networks in the future.
In an expected situation, for example, a user may want to use bidirectional communication services such as video on-demand services and video chatting supplied by a content provider. The user may want to streamingly reproduce data transmitted from the content provider on a personal computer (PC) or a display unit wirelessly connected to the content provider at home.
Transmission of data on IP (Internet Protocol) networks requires control over transmission rates in accordance with states of data reproduction encoding rates, available bands on the IP network, and IP network congestion. General techniques for controlling transmission rates include not only the technique using TCP (Transmission Control Protocol) having data arrival reliability, but also the technique using RTP (Real-time Transport Protocol) defined in highly realtime RFC (Request For Comment) 1889 (e.g., TFRC (TCP-Friendly Rate Control) defined in RFC3448). These techniques are constructed to aim at wired networks with small communication errors.
Generally, a radio network may experience multi-path propagation due to reflected waves from various obstacles. According to the transmission channel characteristic (communication channel characteristic), propagation delay differences cause frequency selective fading that distorts frequency characteristics within transmission bands to remarkably vary or degrade communication states (communication quality).
By contrast, a radio network area is formed between a sending party and a receiving party and is composed of a radio base station and a radio terminal. In order to improve remarkable variations or degradation of communication states, the radio network area is provided with techniques (radio link control) such as antenna diversity, error resistive bit coding, and error packet retransmission.
Even though these techniques are provided, radio communication states or ambient environment degrades communication states such as an increase in packet error rates (radio packet error rates) or Round Trip Time (RTT) during radio communication for a short or long period of time. Such degradation of the communication state is exceptional for the above-mentioned techniques of controlling wired network transmission rates. As a result, the degraded communication state causes congestion in the radio communication and degradation or instability of the data transmission quality (transmission rate (sending rate), transmission delay, etc.). After the radio communication state recovers, the transmission rate recovery delays. Accordingly, the above-mentioned techniques of controlling wired network transmission rates are improper for the streaming reproduction.
FIGS. 1A through 1C show examples of indoor experiment on a radio LAN. With reference to these diagrams, the following describes communication situations of controlling transmission rates according to the transmission rate control technique using the RTP operating on the UDP (User Datagram Protocol) under fading environment.
FIG. 1A shows temporal changes of radio packet error rates (%). FIG. 1B shows temporal changes of transmission rates (Mbps). An upper part of FIG. 1C shows temporal changes of RTT (ms). A lower part of FIG. 1C shows temporal changes of loss rates of packets (packet loss rates) (%). In FIGS. 1A through 1C, the abscissa represents time (s).
As shown in FIG. 1A, several states correspond to the radio packet error rates at the boundary of approximately 20%: a degraded state having large values for a short period, less than several hundreds of milliseconds; a degraded state having large values for a long period, ranging from several hundreds of milliseconds to several seconds; and a normal state having small values. The boundary and values indicate specific tendencies depending on fading situations and radio chip algorithms.
In FIG. 1A, a high radio packet error rate for one second or longer occurs approximately at the time point of 42 seconds (circle A1 in FIG. 1A) to decrease the corresponding throughput (transmissible effective rate) for improving the radio network. As shown in FIG. 1C, the RTT and the packet loss rate increase accordingly (circles C1 and D1 in FIG. 1C). As a result, the transmission rate control technique using RTP decreases the transmission rate as the RTT and the packet loss rate increase.
Afterwards, as shown in FIG. 1A, approximately at the time point of 44 or 45 seconds, the long degrading radio state is restored to the normal state with a low error rate (point A2 in FIG. 1A). Also in this case, it takes approximately three or four seconds b1 for the transmission rate to resume a state (point B2 in FIG. 1B) equivalent to the state before the degraded radio state. This is because the AIMD (Additive Increase, Multiplicative Decrease) algorithm is used to gradually increase the transmission rate for recovery.
Similarly, in FIG. 1A, a high radio packet error rate for one second or longer occurs approximately at the time point of 55 seconds (circle A3 in FIG. 1A). As a result, the throughput for the radio area decreases. As shown in FIG. 1C, the RTT and the packet loss rate increase accordingly (circles C2 and D2 in FIG. 1C). Also in this case, the transmission rate decreases as the RTT and the packet loss rate increase (circle B3 in FIG. 1B). The transmission rate remains low approximately at the time point of 57 seconds (point A4 in FIG. 1A) where the radio packet error rate is restored to the normal state. It takes approximately 10 seconds b2 for the transmission rate to be restored (point B4 in FIG. 1B).
As a result, the transmission rate is controlled based on the transmission rate control technique using the RTP in FIGS. 1A through 1C. Increasing the RTT (points C1 and C2 in FIG. 1C) causes irregular framing in a streamed image. Afterwards, remarkable degradation occurs when the transmission rate decreases (between points B1 and B2 and between points B3 and B4 in FIG. 1B).
As mentioned above, the transmission rate control technique using the RTP causes discrepancy between the transmission rate and the throughput for the radio area during a long degraded radio state. The RTT and the packet loss rate increase to remarkably decrease the transmission rate. In addition, the transmission rate slowly recovers after the radio state recovers. Because of these two factors, that control technique is inappropriate for streaming reproduction.
To solve this problem, there is a demand for a transmission rate control technique that has a congestion control function requested for wired networks, complies with the above-mentioned transmission channel characteristics specific to radio networks and effects of the control provided for radio networks, and provides high-performance and stable data transmission quality.
It is desirable to possibly avoid changes in the existing system construction such as introducing a new apparatus.
For example, a possible transmission rate control technique compliant with radio networks determines a congestion state and a degraded radio state based on the RTT, the packet loss rate, and the radio packet error rate. To correct degraded radio states, there is the technique that maintains and stabilizes the transmission rate (e.g., see JP 2001/160824).
However, the technique disclosed in JP 2001/160824 gives no consideration to the radio link control such as the above-mentioned packet retransmission performed on radio networks, thus causing congestion during radio communication.
According to the other techniques (e.g., see JP 2004/153616 and JP 2004/153619), a radio communication terminal determines the radio communication transmission rate using control information such as DRC (Data Rate Control) in the 1xEV-DO cellular packet network system and transmits the transmission rate to a data delivery apparatus. The techniques disclosed in JP 2004/153616 and JP 2004/153619 cannot be applied to radio LANs that are provided with no protocol for transmitting control information such as DRC. Further, the techniques disclosed in JP 2004/153616 and JP 2004/153619 give no consideration to the congestion control for wired and radio communications.
According to yet another technique, a relay node on the wired network converts data encoding rates depending on degradation of radio communication states detected by using the packet loss rate to adjust rates of transmission to the radio base station. In this manner, the relay node prevents a delay in data arrival from increasing. That is, the technique separates the radio communication from the wired communication for control (e.g., see JP 2004/15761).
However, the technique disclosed in JP 2004/15761 uses the packet loss rate to detect degradation of communication states, thus slowing down the response time of the transmission rate control. The system using this technique requires a relay node.
Moreover, JP 2001/160824, JP 2004/153616, JP 2004/153619 and JP 2004/15761 provide no control over radio communication states in consideration for the long-term and short-term states discussed with reference to FIGS. 1A to 1C.